FIG. 1 is a block diagram of a network structure of UMTS (universal mobile telecommunications system) to which a related art and the present invention are applicable.
Referring to FIG. 1, a universal mobile telecommunications system (hereinafter abbreviated UMTS) mainly includes a user equipment (hereinafter abbreviated UE), a UMTS terrestrial radio access network (hereinafter abbreviated UTRAN), and a core network (hereinafter abbreviated CN).
The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). And, the RNS includes one radio network controller (hereinafter abbreviated RNC) and at least one base station (hereinafter called Node B) managed by the RNC. And, at least one or more cells exist in one Node B.
FIG. 2 is an architectural diagram of a radio interface protocol between UE (user equipment) and UTRAN (UMTS terrestrial radio access network) based on the 3GPP radio access network standard.
Referring to FIG. 2, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer and horizontally includes a user plane for data information transfer and a control plane for signaling transfer.
The protocol layers in FIG. 2 can be divided into L1 (first layer), L2 (second layer), and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The respective layers in FIG. 2 are explained as follows.
First of all, the physical layer (hereinafter named PHY) as the first layer offers an information transfer service to an upper layer using a physical channel. The physical layer PHY is connected to a medium access control (hereinafter abbreviated MAC) layer above the physical layer PHY via a transport channel. And, data are transferred between the medium access control layer MAC and the physical layer PHY via the transport channel. Moreover, data are transferred between different physical layers, and more particularly, between one physical layer of a transmitting side and the other physical layer of a receiving side via the physical channel.
The medium access control (hereinafter abbreviated MAC) layer of the second layer offers a service to a radio link control layer above the MAC layer via a logical channel.
The radio link control (hereinafter abbreviated RLC) layer of the second layer supports reliable data transfer and is operative in segmentation and concatenation of RLC service data units sent down from an upper layer. Hereinafter, the service data unit will be abbreviated SDU.
A radio resource control (hereinafter abbreviated ‘RRC’) layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers to be in charge of controlling the logical, transport and physical channels (hereinafter, the radio bearer will be abbreviated RB). In this case, the RB means a service offered by the second layer for the data transfer between the UE and the UTRAN. And, the configuration of RB means a process of regulating characteristics of protocol layers and channels necessary for offering a specific service and a process of setting their specific parameters and operational methods, respectively.
RRC connection and signaling connection are explained in detail as follows.
First of all, a UE (user equipment) needs to make an RRC connection to a UTRAN to initiate communications and to make a signaling connection to a CN. The UE exchanges UE dedicated control information with the UTRAN or CN via the RRC and signaling connections. FIG. 3 is a flowchart of a process for transmitting messages exchanged between UE and RNC for an RRC connection and transmitting an IDT (initial direct transfer) message for a signaling connection.
Referring to FIG. 3, in a process for an RRC connection, a UE transmits an RRC connection request message to an RNC (S310), the RNC transmits an RRC connection setup message to the UE in response to the RRC connection request message (S320), and the UE transmits an RRC connection setup completion message to the RNC (S330). After successful completion of the above process, the RRC connection is established between the UE and the RNC. After the RRC connection has been established, the UE initiates a process for establishing a signaling connection by transmitting an IDT message (S340).
A random access channel (RACH) as one of transport channels of the asynchronous mobile communication system, WCDMA is explained as follows.
RACH is used in transmitting data having a short length in uplink. And, an RRC message such as an RRC connection request message, a cell update message, a URA update message and the like is transmitted via RACH. A logical channel CCCH (common control channel), DCCH (dedicated control channel) or DTCH (dedicated traffic channel) can be mapped to RACH that is one of transport channels. And, the transport channel RACH is mapped to a PRACH (physical random aces channel) that is one of physical channel.
FIG. 4 is a diagram for explaining a preamble and message transferred via a PRACH that is one of physical channels.
Referring to FIG. 4, the PRACH as one of uplink physical channels is divided into a preamble part and a message part.
The preamble part performs a power ramping function of adjusting a proper transmission power used for a message transmission and a function of preventing collisions between several user equipments.
And, the message part plays a role in transmitting MAC PDU (protocol data unit) to be delivered to a physical channel from a MAC layer.
If a UE's MAC layer instructs a UE's physical layer to make a PRACH transmission, the UE's physical layer firstly selects one access slot and one signature and then transmits a PRACH preamble to a base station (Node B) in uplink. The preamble is transmitted during an access slot interval of 1.33 ms. One signature is selected from sixteen kinds of signatures and is then transmitted for a first predetermined duration of the access slot.
If the UE transmits the preamble, the base station transmits a response signal via a AICH (acquisition indicator channel) that is one of downlink physical channels. The AICH transmitted in response to the preamble carries the signature selected by the preamble for a second predetermined duration of an access slot corresponding to the former access slot having carried the preamble. In this case, the base station transmits an affirmative response (ACK) or a negative response (NACK) to the UE via the signature carried by the AICH.
If the UE receives the ACK, the UE transmits a message part having a length of 10 ms or 20 ms using an OVSF code corresponding to the transmitted signature.
If the UE receives the NACK, the UE's MAC layer instructs the UE's physical layer to make the PRACH transmission again after a proper duration.
Meanwhile, if the UE fails in receiving AICH corresponding to the transmitted preamble, the UE transmits a new preamble after the selected access slot with a power one step higher than that of the former preamble.
FIG. 5 is a structural diagram of the AICH that is one of downlink physical channels.
Referring to FIG. 5, the AICH transmits a 16-symbol signature Si (i=0 . . . 15) for an access lot having a 5120-chip length. In this case, a UE selects an arbitrary signature Si from signatures S0 to S15 and then transmits the signature for a first 4096-chip length while setting the rest 1024-chip length to a transmission power ‘OFF’ interval of transmitting no symbol.
Meanwhile, a preamble part of the PRACH transmits 16-symbol signature Si (i=0 . . . 15) for a first 4096-chip length in a way similar to that shown in FIG. 4.
FIG. 6 is a block diagram of a network structure of E-UMTS (evolved universal mobile telecommunications system) to which a related art and the present invention are applicable.
Referring to FIG. 6, an E-UMTS is the system evolving from the conventional UMTS and its basic standardization is currently handled by the 3GPP.
First of all, E-UMTS network includes a user equipment (hereinafter abbreviated UE), a base station (hereinafter named Node B), a control plane server (hereinafter abbreviated CPS) performing a radio control function, a radio resource management (hereinafter abbreviated RRM) performing a radio resource management function, a mobility management entity (hereinafter abbreviated MME) performing a UE's mobility management function and an access gateway (hereinafter abbreviated AG) connected to an external network by being located at an end of the E-UMTS network. And, at least one cell exists in one Node B.
Layers of a radio interface protocol between UE and network can be classified into a first layer L1, a second layer L2 and a third layer L3 based on three lower layers of OSI (open system interconnection) reference model widely known in communication systems.
A physical layer belonging to the first layer offers an information transfer service using a physical channel. And, a radio resource control (hereinafter abbreviated RRC) located at the third layer plays a role in controlling radio resources between UE and network. For this, RRC layers enable RRC messages to be exchanged between the UE and the network. And, the RRC layers can be located at Node B, CPS/RRM and MME by having its function distributed.
FIG. 7 is an architectural diagram of a control plane of a radio interface protocol between UE (user equipment) and UTRAN (UMTS terrestrial radio access network) based on the 3GPP radio access network standard.
Referring to FIG. 7, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer and horizontally includes a user plane for data information transfer and a control plane for signaling transfer.
The protocol layers in FIG. 7 can be divided into L1 (first layer), L2 (second layer), and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The respective layers of a radio protocol control plane shown in FIG. 7 and a radio protocol user plane shown in FIG. 8 are explained as follows.
First of all, the physical layer as the first layer offers an information transfer service to an upper layer using a physical channel. The physical layer PHY is connected to a medium access control (hereinafter abbreviated MAC) layer above the physical layer via a transport channel. And, data are transferred between the medium access control layer and the physical layer via the transport channel. Moreover, data are transferred between different physical layers, and more particularly, between one physical layer of a transmitting side and the other physical layer of a receiving side via the physical channel.
The medium access control (hereinafter abbreviated MAC) layer of the second layer offers a service to a radio link control layer above the MAC layer via a logical channel.
The radio link control (hereinafter abbreviated RLC) layer of the second layer supports reliable data transfer. A function of the RLC layer can be implemented in a function block included in the MAC layer. In this case, the RLC layer does not exist independently.
A PDCP layer of the second layer performs a header compression function for reducing unnecessary control information to efficiently transmit data, which is transmitted using such an IP packet as IPv4 or IPv6, in a radio section having a relatively small bandwidth.
A radio resource control (hereinafter abbreviated ‘RRC’) layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers (hereinafter abbreviated RBs) to be in charge of controlling the logical, transport and physical channels. In this case, the RB means a service offered by the second layer for the data transfer between the UE and the UTRAN.
As a downlink transport channel carrying data to UE from network, there is BCH (broadcast channel) carrying system information and DL_SCH (downlink shared channel) carrying user traffic or control message.
As an uplink transport channel carrying data to network from UE, there is RACH (random access channel) carrying an initial control message and UL_SCH (uplink shared channel) carrying user traffic or control message.
However, in the related art access process, a step of confirming a location of UE and a step of allocating a necessary resource to the UE and the like are sequentially carried out to increase a time taken for an initial access setup process.